Magnesium base alloys



Patented July 22, 1952 MAGNESIUM BASE ALLOYS Alfred C. Jessup, CliftonJunction, near Manchester, England, assignor to Magnesium ElektronLimited, Clifton Junction, near Manchester, England, a British companyNo Drawing. Application May 21, 1951, Serial No. 227,541. In GreatBritain June 2, 1950 y This invention relates to magnesium'base al-,loys.

3 Many attempts have been made to produce magnesium base alloys havinghigh resistance to creep atelevated temperatures. To this end, it hasbeen proposed to use binary alloys containing up to about cerium, or toproduce alloys containing cerium together with certain other elements,for example, manganese, cobalt and calcium. While such additions ofcerium have proved effective in increasing resistance to creep, thealloys in general are unsatisfactory, particularly because they tend tobe too brittle at room temperature. v

"It has recently been proposed to utilise magnesiumbase alloyscontaining up to about 1% zirconium together with about 1 to 4% cerium,and these alloys have been found to have better creep resistance atelevated temperatures and improved properties at room temperature.

With a view to modifying properties of alloys containing zirconium andrare earth metals, I have added zinc,- and find that, in addition tofacilitating the production of sand castings, this addition results in amarked improvement in creep properties at temperatures over 250 .0.However such alloys, although still possessing reasonably goodresistance to creep at loads of the order of 1 ton per square inch attemperatures of 300 C. or over, are subject to an unduly high rateofcreep in the early stages. The overall creep rate of such alloys atloads over 1 ton per square inch at temperatures over 300 C. is such asto make these alloys unsatisfactory for many applications.

I have therefore endeavoured to find an alloy possessing the followingcombination of properties:

1. High creep resistance upv to and above 300 C. inthe initial as wellas later stages of test.

- 2; Absence of. the onset of tertiary creep up to a testing time of. atleast 1000 hours.

3. Good tensile strength at normal atmospheric temperatures. I

4. Sufficient elongation at room temperatures.

5. Good corrosion resistance.

6. Good casting properties.

I have now ascertained that this combination of properties including aquite remarkably high creep resistance up to and above 300 0., isobtained with alloys containing thorium and zinc in suitable relativeproportions in addition to zirconium. Alloys with satisfactoryresistance to creep at temperatures of 300 C. or over can also be madeby adding rare earth metals to the aforev- Claims. (01. 75-9168) 2mentioned alloying constituents, namely, thorium, zinc and zirconium.

The zirconium content should be 0.1 to 0.9 per cent, and at least 0.1%and preferably at least 0.4 per cent should be present in the solublecondition i. e. in a condition which is readily soluble (together withthe magnesium) in an aqueous solution of hydrochloric acid consisting of30 cos., of HCl (specific gravity 1.16) to 85 cos. of water, sufficientacid being added during dissolution to maintain the initialconcentration.

The proportion of thorium for the purpose of the present invention isnot less than nine tenths of the proportion of the zinc and not morethan ;three times the quantity of zinc. .The total quan-I- 'tity ofthorium and zinc together is not greater than 10%. The quantity ofthorium is also not greater than nine tenths of the zinc percentage plus2%% i. e. if the zinc is 2% the thorium will not exceed 4.55%. Inaddition the thorium should lie between 1 and 6% and the zinc between.A; and 5%. Preferably the thorium percentage is not greater than 1 /2plus nine tenths of the zinc percentage and preferably not less than 1.4times the zinc percentage less 1.5%. Preferably also the thorium contentis between 2 and 5.75% and the zinc between 0.75 and 4.75%. A lower orhigher percentage of zinc does not offer the desirable high creepresistance, and a higher percentage of zinc harmfully affects otherproperties of the alloy, such as elongation at atmospheric temperatures.

The present invention provides alloys having a creep resistance attemperatures of the order of 300 to 320 (3., much higher than in othermagnesium base alloys and in fact much higher than commonly usedaluminium base alloys and this high creep resistance, which is achievedin combination with good tensile strength at normal temperatures, andother sufficiently good mechanical properties, is a remarkable andunexpected advance in this art.

The alloys of the present invention preferably contain no other alloyingingredients than those abovementioned, in particular for example, silverand copper, which if included at all should not exceed 1% in the case ofsilver and preferably less than 0.05%, whilst the copper should notexceed 1% and is preferably less than 0.02%.

A cast test bar made from alloys according to the present invention andcast according to British Standards'Specification No. L101, Figure 1,when heat treated at 315 ,C., for 24 hours and subjectedto creep test at315 C., under a load of 1.5 tons will have a creep strain less than 2%and tion also provides alloys having themaximum corrosion resistance inaqueous solutions of sodium chloride.

By way of example, the following alloymam be cited:

Per cent Rare earth metals, up to 4 Baryllium, up to 0.1 Calcium, up to0.2

Silver. up to 1 Copper, up to 1 Mercury, up to 3 Lead, up to 1Tha-llium, up to 1 Lithium, up to 12 the magnesium content being atleast 85%.

3..An alloy'as' claimed in claim 1 containing 'aisoiat least oneof thefollowing:

.. Per cent Silver, up to 0.05 Copper, up to 0.02

Zirconium -1; 0.7v

Thorium alla1- =1 1 1e e 111e1 11 3.1 Zinc a. Y..:.. Magnesium 1 balanceCast test bar of the above composition made accordim;v to. theaforesaid. British: Standards Specification whenheat treated at 315 C.,for 2a. hours hadthe following. properties. atxroom temperatures:

Elongation per cent on 2 inches Ultimate Tensile I Proof Stress .1%Strength Tons per Tons per sq.

square inch inch On thesarne alloy the percentage creep strain after 500hours at 315 C., was 0.30 under a stress of 1.5 tons per square inch.

Other ingredients. which can be usefully tolerated in the alloys are thefollowing;

Lithium, upto 12 The total proportion of all alloying'ingredientsotherthan magnesium should not exceed 15 per cent. I

'Il-ie all-oys of the present invention are-specially useful for thema-nufacture of partsusedin or adiac'e'nt'to engines which parts arestressed and subject to temperatures of over 250 C. in use.

1; A magnesium base alloy *consistin'g'essentially of zirconiuminamountbetween 0.1" and 0.9%", at least 0.1% being presentin solution in thealloy, thoriflmbetWeen-1;and-6%' andjzi'nc between-0:5 and-5%,thep'ercen-tage of thorium being between ninetenthsand three times thepercentage ofzinc but not exceeding nine-tenths of "t-l' efzinc contentbyr-more than, 2%%'',' the thoriumjand zinc together notexceedingifle'e, the balance-being magnesium;

2. An'alloyas'claimed claim 1 containing also atleast one of thefollowing:

4. An alloy as claimed in claim 1 containing at least one of the rareearth metals in amount between 0.1 and 0.7%.

5.,A magnesium Ibase alloy consisting of essenmany zirconium in amountbetween 0.1 and 0.9% at least 0.1 being in solution in the alloy, thorifum between land 6%, and zinc between 0.5 and 57%" the ercentage of'thoriunibeing between ninetenthsand three times thepercentag'e ofzincihut not'ex'ceedin'g nine-tenths of the-zinc content by more than 1/2 nor falling short of 1.4 times the percentage of zinc by more. than1.5 per cent, the thorium and zinc together not exceeding 10 the balancebeingmagl lesium. v

6'. An alloy as. claimed in claim 5 containing also at least oneof thefollowing:

the magnesiur'ncontentbeing at least 7: An' alloy as claimed in claim 5"containing also at least one of the-following: V

ALFREDO. JESSUP.-'

REFEnENoEscI-mn The following references are of 'rec'ord in the file ofthis patent: V

UNITED STATES: PATENTS Number V OTHER. REFERENCES "senat 3fi 9g749;sauerwald et al. (A. P. 0.6:, published-June'15,194'3;

1. A MAGNESIUM BASE ALLOY CONSISTING ESSENTIALLY OF ZIRCONIUM IN AMOUNTBETWEEN 0.1 AND 0.9%, AT LEAST 0.1% BEING PRESENT IN SOLUTION IN THEALLOY, THORIUM BETWEEN 1 AND 6% AND, ZINC BETWEEN 0.5 AND 5%, THEPERCENTAGE OF THORIUM BEING BETWEEN NINE-TENTHS AND THREE TIMES THEPERCENTAGE OF ZINC BUT NOT EXCEEDING NINE-TENTHS OF THE ZINC CONTENT BYMORE THAN 2 3/4%, THE THORIUM AND ZINC TOGETHER NOT EXCEEDING 10%, THEBALANCE BEING MAGNESIUM.
 2. AN ALLOY AS CLAIMED IN CLAIM 1 CONTAININGALSO AT LEAST ONE OF THE FOLLOWING: